=over

=item log EXPR
X<log> X<logarithm> X<e> X<ln> X<base>

=item log

Returns the natural logarithm (base I<e>) of EXPR.  If EXPR is omitted,
returns the log of L<C<$_>|perlvar/$_>.  To get the
log of another base, use basic algebra:
The base-N log of a number is equal to the natural log of that number
divided by the natural log of N.  For example:

    sub log10 {
        my $n = shift;
        return log($n)/log(10);
    }

See also L<C<exp>|/exp EXPR> for the inverse operation.

=back